Microwave impedance-matching network

ABSTRACT

In preferred form, a matching network includes a transmission line comprising a pair of parallel inner conductors symmetrically located in an outer conductor enclosure for supporting odd and even modes of propagation. Impedances to be matched are connected between adjacent one ends of the inner conductors and the enclosure. First and second sections of the transmission line, measured from the one ends of the conductors, are formed by short circuiting the inner conductors together and both inner conductors to the enclosure, respectively, at points that are spaced from the one ends of the conductors. The first transmission line section supports both the even and odd modes of propagation while the second line section primarily supports only the even mode of propagation. The positions of the short circuits are moved along the inner conductors in order to match the impedances. In an alternate embodiment, the network includes a pair of parallel inner conductors symmetrically located in a first cylindrical conductor, the latter being coaxially supported in a second cylindrical conductor. First and second sections of short circuited transmission line are formed by short circuiting the cylinders together and by short circuiting both inner conductors to the first cylinder, respectively. The positions of the short circuits are separately moved along the cylinders in order to match impedances that are connected between associated inner conductors and the second cylinder. Stripline versions of these networks are also disclosed.

United States Patent 1191 Rogers 1451 July 10,1973

[ MICROWAVE IMPEDANCE-MATCHING NETWORK [75] Inventor: Robert G. Rogers,Los Altos, Calif.

[73 Assignee: GTE Automatic Electric Laboratories Incorporated,Northlake, Ill.

[22] Filed: Nov; 1, 1971 [21] Appl. No.: 194,383

Related US. Application Data [63] Continuation-impart of Ser. No.[15,449, Feb. 16,

1971, Pat. N0. 3,699,475.

Barrett-Microwave Printed CircuitsA Historical Review in IRETransactions on Microwave Theory & Techniques Volume M'IT-3, March 1955;pp. 1-3 & 6 1

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Marvin NussbaumAttorney- K. Mullerheim, Leonard R. Cool et al.

[5 7 ABSTRACT In preferred form, a matching network includes atransmission line comprising a pair of parallel inner conductorssymmetrically located in an outer conductor enclosure for supporting oddand even modes of propagation. Impedances to be matched are connected between adjacent one ends of the inner conductors and the enclosure. Firstand second sections of the transmission line, measured from the one endsof the conductors, are formed by short circuiting the inner conductorstogether and both inner conductors to the enclosure, respectively, atpoints that are spaced from the one ends of the conductors. The firsttransmission line section supports both the even and odd modes ofpropagation while the second line section primarily supports only theeven mode of propagation. The positions of the short circuits are movedalong the inner conductors in order to match the impedances. In analternate embodiment, the network includes a pair of parallel innerconductors symmetrically located in a first cylindrical conductor, thelatter being coaxially supported in a second cylindrical conductor.First and second sections of short circuited transmission line areformed by short circuiting the cylinders together and by shortcircuiting both inner conductors to the first cylinder, respectively.The positions of the short circuits are separately moved along thecylinders in order to match impedances that are connected betweenassociated inner conductors and the second cylinder. Stripline versionsof these networks are also disclosed.

16 Claims, 7 Drawing Figures PATENTEU JUL 1 0 SHEU 1 (IF 3 INVENTOR.ROBERT G. ROGERS BY W 44 AGENT PATENIEUJUL 1 mm SHEU 2 BF 3 INVENTOR.ROBERT G. ROGERS BY Mfi AGENT MICROWAVE IMPEDANCE-MATCHING NETWORKREFERENCE TO COPENDING APPLICATION This case is a continuation-in-partof my copending U.S. Pat. application, Double-Mode Tuned MicrowaveOscillator, Ser. No. 115,449, filed Feb. 16, 1971 now U.S. Pat. No.3,699,475, issued Oct. 17, 1972.

BACKGROUND OF INVENTION This invention relates to tuning circuits andmore particularly to a tunable microwave impedance matching network.

An impedance matching network is a two-port device that is employed totransform a given value of impedance connected across one port to adifferent value of impedance connected across the other port or to matchtwo given impedances having different values. Such networks are oftenmade adjustable in order to transform the value of the given impedanceinto whatever value of impedance is required, e.g., so as to producemaximum output power from an oscillator including a semiconductor devicein which wide electrical tolerances are common. Prior art adjustableimpedance matchingnetworks include dielectric slugs in a coaxialtransmission line, a coaxial transmission line having a movableeccentric center conductor, and tuning stubs short circuited across atransmission line. The former two matching networks are limited in therange of impedances that can be matched. The triple-stub tuner comprisesthree short circuited stubs that are spaced a quarter wavelength apartalong a transmission line at the operating frequency of the tuner.Although this tuner is commonly usedfor impedance matching, it has thedisadvantage of being a fixed frequency device for operating at a singlefrequency or over a very narrow band of frequencies. A physicallydifferent tuner is required to match the same impedances at a differentfrequency. Also, tuning of this prior art device is complicated by thefact that there are three controlsor plungers to adjust, of which twomay be maintained equal. Thus, it is necessary to vary three separatecontrols or to gang two of the plungers together.

An object of this invention is the provision of an improved impedancematching network.

Another object is the provision of an impedance matching network capableof matching impedances over a broad range of impedance values and over abroad band of frequencies.

SUMMARY OF INVENTION Briefly, two short circuited transmission linesections, at least one of which supports both 'odd and even modes ofpropagation, are electrically connected at one ends thereof that arespaced from the short circuits. Two impedances to be matched areconnected across conductors of the line sections at their connectionpoint. The impedances are matched by changing the positions of the shortcircuits and thus the lengths of the line sections between theimpedances and the short circuits.

DESCRIPTION OF DRAWINGS This invention will be more fully understoodfrom the following detailed description thereof, together with thedrawings in which:

FIG. 1 is a perspective view of a preferred embodiment of this inventionwith the top and side walls partically cut away to show the internalconstruction thereof;

FIG. 2 is a perspective view of a stripline version of the tuner in FIG.1 with top plates broken away to show the internal construction thereof;

FIG. 3 is a schematic circuit diagram representing the electricalequivalent circuit of the tuner in FIG. 2 with a load admittance Yconnected thereto;

FIG. 4 is a perspective view of an alternate embodiment of thisinvention with the outer conductor cut away to show the internalconstruction thereof;

FIG. 5 is a greatly enlarged top view, mostly in section, of anotherembodiment of this invention;

FIG. 6 is a schematic circuit diaphragm representing the electricalequivalent circuit of the tuner in FIG. 5 with a load admittance Y,connected thereto; and

FIG. 7 is an exploded section view of the stripline version of the tunerin FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, apreferred embodiment of this invention comprises a pair of metal rodconductors 4 and 5 that are mounted in a square metal box or enclosure 6which is a ground plane. The enclosure may also be cylindrical. The rodconductors preferably are of the same diameter and symmetrically locatedin the enclosure 6, although this is not necessary. This tuner is a twoport network having ports corresponding to the coaxial connectors 7 and8 that are mounted on the end wall 9 of theenclosure. The connectors areconnected to the one ends of associated conductors 4 and 5 and wall 9.The other ends of the conductors are supported in the end wall 10 of theenclosure.

The conductors 4 and 5 are short circuited together at a distance I,from the end wall 9 by a metal rod 12 having conductive sleeves l4 and15 connected to the ends thereof. These sleeves are coaxial with theconductors 4 and 5. Spring fingers on sleeves l4 and 15 electricallycontact the associated conductors 4 and 5. The conductors are also shortcircuited together and to enclosure 6 at a distance 1 1 from end wall 9by a movable wall 16. Spring fingers 17 on the movable wall contact theground plane enclosure 6. Metal sleeves 18 and 19, which are mounted inwall 16 coaxial with conductors 4 and 5, respectively, have springfingers which provide a sliding electrical contact with the associatedconductors.

This transmission line comprising conductors 4 and 5 and the enclosure 6supports both even and odd modes of propagation. The conductors 4and 5for the even mode have currents thereon that are in phase at adjacentpoints across the conductors, i.e., the conductors are everywhere at thesame potential for the even mode. The currents for the odd mode,however, are out-of-phase at adjacent points across conductors 4 and 5.Thus, the short circuit produced by rod 12 has no effect on the evenmodes on conductors 4 and 5. Rod 12 is a short circuit, however, for theodd mode. Rod 12 and the length 1 of transmission line are referred toas an odd mode short circuit and an odd mode transmission line,respectively, although this length 1 of line actually supports both oddand even modes. The length I, of line, however, normally only supportseven modes. Since wall 16 short circuits conductors 4 and 5 together aswell as to the ground plane 6, the movable wall 16 is a combination oddand even mode short circuit. The wall 16 and length 1, +1 oftransmission line are referred to hereinafter, however, as an even modeshort circuit and an even mode transmission line, respectively.

A rod 21 is rigidly connected to wall 16 for moving the latter wall andthereby changing the position of the even mode short circuit and thelength 1 of the conductors. A rod 22 extends through the walls and 16 ofthe enclosure and is centered between conductors 4 and 5. The rod 22 isrigidly secured to rod 12 and is used to change the position of the oddmode short circuit produced by the latter and the length 1 of the oddmode transmission line. Although moving rod 12 causes the lengths l andof conductors 4 and 5 to both vary, this is not a problem in practicesince the two controls are adjusted together to match impedancesconnected to the coaxial connectors 7 and 8. The rod 12 has theadvantage of suppressing undesirable odd mode resonances that mightoccur on the conductors between the short circuits provided by rod 12and wall 16 when the length 1 of line is a half wavelength long at theoperating frequency of the tuner. The rod 22 may be made of electricallyconductive or dielectric material. Alternatively, rod 22 may be aconductor contacting both conductors 4 and 5 over the lengths 1 thereofbetween rod 12 and wall 16.

In a tuner for operating over a broad band of frequencies, the lengths land 1 of transmission line are preferably each made a half wavelengthlong at the lowest frequency of operation. The tuner can then beemployed to match any impedances at frequencies greater than thisinitial lowest design frequency value since all possible values ofimpedance may be obtained with a transmission line section that is ahalf wavelength long.

In operation, the impedances to be matched by the network in FIG. 1 areconnected to connectors 7 and 8, i.e., between conductors 4 and 5 andthe ground plane 6. The network is tuned to match these impedances byphysically moving the positions of the short circuit elements 12 and 16along the conductors. Since the values of the impedances that are to bematched may be unknown, adjustment of the lengths l and 1 of conductors4 and 5 is made by moving elements 12 and 16 so as to give a desiredresult such as maximum power output of an oscillator or amplifier asindicated on a power meter.

Referring now to FIG. 2, a stripline version of the tuner in FIG. 1 isshown wherein similar elements are designated by primed referencecharacters in FIG. 2. This stripline tuner comprises a pair of striplineconductors 4' and 5' formed on a lower dielectric block 26 which has abottom ground plane plate 27 secured thereto. The top section 28 of thistuner comprises an upper dielectric block 29 having a top ground planeplate 30 bonded thereto. Section 28 is placed over the conductors 4' and5 and secured to the lower dielectric block, e.g., by screws (notshown). Metal plates 31,

' 32 and 33, 34 (the latter plate 34 not shown) are bonded to the sidesof the associated dielectric blocks 26 and 29. The two ground planeplates 27 and 30 are electrically interconnected through side plates 3134. The conductors 4 and 5' areparallel to each other and ground planeplates 27 and 30. An odd mode short circuit is formed on conductors 4'and 5' at a distance 1 from the one end 35 of the dielectric blocks by athin metal strip 12' which is spaced away from the metal side'plates 3134. The conductors are also short circuited together and to the groundplanes at a distance 1 from the short circuit element 12' by a thinmetal strip 16 to form an even mode short circuit. The metal strip 16contacts both of the conductors 4' and 5' and the side plates 31 34.Impedances that are to be matched by the network are connected to ports7' and 8, i.e., between conductors 4' and 5 and plates 27 and 30.

The network is tuned to match these impedances connected to ports 7 and8' by moving the position of the short circuiting metal strips 12' and16 along conductors 4' and 5'. In this stripline tuner, the top section28 thereof must be removed to change the positions of the shortcircuits. Alternatively, a modified form of the strip transmission linetuning devices disclosed in U.S. Pat. No. 3,210,697 by B. H. Comstockmay be employed to accomplish this function.

The operation of an impedance matching network embodying this inventionwill now be analyzed in relation to a microstrip transmission linedevice similar to the stripline device in FIG. 2 wherein the dielectricis air. The electrical equivalent circuit of the tuner in FIG. 2 and anair-dielectric microstrip transmission line tuner is a symmetrical wcircuit comprising elements 41, 42 and 43, as illustrated in FIG. 3. Theadmittances Y, and Y of the associated elements 41 and 42 are identicalfor a physically symmetrical microstrip circuit (where the lineconductors are of the same size and equally spaced from ground planes 27and 30) and are representable as where Y is the even mode characteristicadmittance of the transmission lines, 0 B1 0 B1 0 and 0 are theelectrical lengths of the associated transmission lines, [3 Z rr/A, 1ris a constant, A is the wavelength at the frequency at which the networkis to operate, and B is the susceptance of the element 41. Theadmittance Y of the element 41 is purely imaginary since the odd andeven mode lines are assumed to be losslessv Since the lengths l, and 1of transmission line are physically and electrically short at microwavefrequencies, this is a resonable assumption. A nonsymmetrical microstripcircuit, e.g., where the parallel conductors are of different sizes,would be defined by an unsymmetrical 1r circuit in which the values ofthe admittances Y and Y were unequal.

The admittance Y of element 43 is representable as where Y, is the oddmode characteristic admittance of the transmission lines and B is thesusceptance of element 43. The characteristic admittances Y and Y of thetransmission lines are related to the size and spacing of the conductors4 and 5 with respect to the ground plane enclosure and are calculated ina manner known in the prior art.

Assuming that a load 44 is connected across port 8 for example, theinputadmittance Y, across the other port 7' is are solved to obtaindefinitions of the susceptances B and B and are representable as i and ai 1/ i L[( t+ 1 t HQ/ 1. t

The quantities underthe radicals in equations (4 and (5) are nevernegative since the conductances G, and 6,, must both be either positiveor negative, i.e., of the same sign. This is because an impedancematching network withpurely reactive elements does not convert apositive impedance to a negative impedance and vice versa. Thus, nomatter what the value of the load admittance Y it will be matched ortransformed to the desired input admittance Y When the given values ofthe load admittance Y and the desired value of the input admittance Y,are known, for example, the susceptances B and B can be determined fromequations (4) and (5 The physical lengths l and 1 of transmission linesrequired to transform the admittance Y to the admittance Y, can then bedetermined from equations (1) and (2). Although these equations indicatethat a change in the length of either I, or 1 changes both of thesesusceptances B and B this is no problem in practice since the lengths land 1 of line are both adjusted together to match theadmittances Y andY,. The foregoing equations are particularly useful in defining amatching network for operating over a small range of impedances andfrequencies.

By way of example, in an impedancematching network similar to thatillustrated in FIG. 1 that was built and tested, the rods 4 and 5 weresymmetricallylocated in a square enclosure 6 having inner dimensions of0.55 by 0.55 inch, the diameters of the rods were 0.125 inch, and thecenter-to-center spacing of the rods was0.208 inch. The odd and evenmode characteristic admittances Y and Y of this experimental tuner were15.4 m mho and 6.9 m mho (i.e., 65 ohm and 145 ohm), respectively. Thesevalues were calculated using equations in"Coupled-Strip-Transmission-Line Filters and Directional Couplers by E.Jonesand J. Bolljahn, [RE Transactions on Microwave Theory andTechnology, Vol. MTT-4, pp. 75-8l, April 1956. These admittance valueswere verified by operating the circuit with a known load impedance 2,,connected to port 7, moving the short circuits 12 and 16 to adjust thelengths l and 1,, of line until the desired input impedance Z, wasindicated on a meter connected to the other port 8, measuring the linelengths l and I and solving equations (1) and (2) for the admittances Yand Y,,,,. The results obtained by these two methods were in reasonable5 agreement indicating that the equations satisfactorily define theoperation of the tuner. This tuner operated satisfactorily over a 2 lbandwidth from 1 GHz to 2 GHz while matching impedances over a broadrange of impedance levels as shown by the Hewlett-Packard 8410A NetworkAnalyzer.

. Referring now to FIG. 4, a tuner embodying a modified form of thisinvention comprises a pair of rod conductors 47 and 48 thataresymmetrically supported in a cylindrical enclosure 49 by a fixed endwall 50 and a dielectric spacer (not shown). A pair of lines 51 and 52define the two ports 53 and 54 of the tuner to which impedances tobematched are connected. Lines 51 and 52 are electrically connected toconductors 47 and 48, respectively, on line AA which is orthogonal tothe longitudinal axis of the enclosure. The lines. 51 and 52 areinsulated from the enclosure by dielectric spacers (not shown). Thedielectric spacer supporting conductors 47 and 48 in the enclosure maybe located, for example, adjacent to lines 51 and 5 2.

A first short circuit isformed on conductors 47 and 48 by a U-shapedconductive element 55 which is insulatedfrom enclosure 49 and spaced adistance 1 from the line AA. The hollow arms 56 and 57 of element 55extend over the ends of conductors 47 and 48, respectively, to form atrombone-like sliding structure for adjustingthe length l oftransmission line between element 55 and line A-A. Spring fingers on thearms 56 and 57 make electrical connection to the associated conductors47 and 48. A rod 58 extends through the endwall 59 of theenclosure andis secured to element 55. The rod 58 is used tochange the position ofthe first or odd mode short circuit on conductors 47 and 48. Rod58 ispreferably made of a dielectric material.

A second shortcircuit is formed on conductors 47 and 48 bya movable wall60 in theenclosure. The wall 60 is electrically conductive and hasspring fingers contacting the inner wall of the enclosure and both ofthe conductors 47 and 48. A rod 61 extends through end wall '50 andissecured to wall 60. The rod 61 is used to change the positionof thesecond short circuit and thus to adjustthe length], of transmission linebetween wall 60 and line A-A. The lengths l and l, of transmission line,which bothsupport odd and even modes, are varied by moving the shortcircuit elements 55 and 60 in order to match impedances connected toports 53 and 54. The operation of the tuners in FIGS. 1 and 4 aredefined by different design equations.

Referring now to FIG. 5, a concentric tuner embodying an alternate formof this invention comprises a pair of conductive rods 65 and 66 that aresymmetrically supported in an inner electrically conductive hollowcylinder 68 (e.g., by dielectric spacers, not shown). The inner cylinder68 is centered in an outer electrically conductive hollow cylinder 69(e.g., by dielectric spacers, not shown). The conductor rods 65 and 66ex- ;tend in both directions in the extensions 71 and 72 of the outercylinder 69 where they are connected to coaxial connectors 73 and 74,respectively, to form a structure that can be connected in series withcoaxial transmission line devices. A more compact tuner structure may bemade by omitting the two coaxial line sections 71 and 72, placingminiature connectors at the ends of the lines 65 and 66, and closing thesection 70 with an end plate (not shown) on line BB which iselectrically connected to the outer conductor 69, is insulated fromcylinder 68, and is the mounting plate and ground plane for theminiature connectors. The lengths of conductors 65 and 66 beyond theline BB are to facilitate connection thereto to external coaxialdevices.

The dimensions and spacings of elements in the sections 70 72 arerelated to th characteristic impedances of the transmission linesthereof as is known in the art. The outer cylinder 69 may have a taper(not shown) over a portion of the length thereof adjacent the junctionof section 70 and sections 71 and 72 when the dimensions of thesesections are different.

An electrically conductive disc 76 is located in the central opening ofthe inner cylinder 68. Spring fingers on disc 76 contact both of theconductors 65 and 66 and the inner cylinder to form a combination oddand even mode short circuit defining a length 1 of transmission line. Arod 77 is connected to the disc 76 and is employed to change theposition of the short circuit produced by the latter and thus to changethe length 1 of transmission line. An electrically conductive ring 78 islocated in the opening between the cylinders 68 and 69. Spring fingerson ring 78 contact the adjacent surfaces of the cylinders. Thus, ring 78is effectively a short circuit defining a length 1 of coaxialtransmission line. Push rods 79 and 80 which are secured to a bar 81 andthe ring 78 provide a convenient mechanism for moving the short circuitelement 78 and changing the length 1 of transmission line. The positionof the short circuit elements 76 and 78 and the lengths of theassociated line sections are varied to match impedances connected to thecoaxial connectors or ports 73 and 74.

The operation of the tuner in FIG. 5 will now be described in relationto the electrical equivalent circuit thereof in FIG. 6 wherein thepoints 83 86, inclusive, in the latter correspond to points designatedby primed reference characters in FIG. 5. A transmission linerepresented by the line of length 1 is described in Microwave Filters,Impedance Matching Networks, and Coupling Structures by G. Matthaei, L.Young and E. Jones, McGraw-Hill Book Company, New York, 1964, pp. 225.The electrical equivalent circuit of this length 1 of transmission lineis a symmetrical 1r circuit comprising elements 87, 88 and 89 betweenpoints 83 and 84 on the conductors, with respect to the inner sheath 68and point 85' thereon. The admittances Y, and Y of elements 87 and 88,respectively, are the same for a strictly symmetrical circuit and arerepresentable as Y, Y jY,, cot [31,, +jB

where Y is the even mode characteristic admittance of the length 1 ofthis transmission line. The admittance Y of element 89 is representableas cuit of the length 1 of transmission line, which is essentially ashort circuited coaxial transmission line comprising the inner and outercylinders, is an element 90 having an admittance Y connected between theinner and outer cylinders, i.e., between the points and 86. Theadmittance Y,, is representable as 0 j 06 cot B s +1 0 where Y is thecharacteristic admittance of the length I, of coaxial transmission line.

The 1r circuit comprising elements 87, 88 and 89 can be transformed to afirst equivalent Tcircuit connected to point 85. The element 90 and theelement of the first equivalent T circuit in series therewith can thenbe represented by a single element to form a second threeelementequivalent T circuit. The latter T circuit can be represented as asecond equivalent three-element 1r circuit having a load 91 connectedacross it to provide an equivalent circuit similar to that in FIG. 3.Equations for this second equivalent 1r circuit that are similar toequations (1) (5) can then be derived. These new equations will definethe operation of the tuner in FIGS. 5 and 6, as was described above inrelation to FIG. 3.

A stripline version of the tuner in FIG. 5 is illustrated in FIG. 7 inan exploded cross section and comprises an inner section 93 and upperand lower outer sections 94 and 95, respectively. The inner section 93is similar to the stripline tuner in FIG. 2 except that the metal strip12' is omitted in FIG. 7. The upper section 94 com prises a dielectricblock 96 having a conductive top ground plane plate 97 and conductiveside plates 98 and 99 bonded thereto. The lower section comprises thedielectric block 100 having a longitudinal groove 101 therein forreceiving the inner section 95. A conductive bottom ground plane plate102 and conductive side plates 103 and 104 are bonded to dielectricblock 100. A metal strip 105 is located between the outer sections 94and 95 and extends over thewidth of the latter for short circuiting theground plane of the inner section to the ground plane of the outersection. This device must also be disassembled to change the position ofthe short circuits therein and thus to accomplish tuning thereof.

Although this invention has been shown as described in relation topreferred embodiments thereof, variations and modifications thereof willbe apparent to those skilled in the art. For example, the lengths ofappropriate lines may be formed of any transmission line capable ofsupporting odd and even modes of propagation. Also, unwanted odd moderesonances that may occur on the length 1 of the conductors in FIG. 1,for example, may be suppressed by placing an additional short circuitsuch as a metal clip between conductors 4 and 5 approximately halfwaybetween rod 12 and wall 16. A nonsymmetrical network may also beproduced, for example to match a very high impedance to a very lowimpedance, by employing conductors 4 and 5 having different diameters orwhich are nonsymmetrically located in an outer conductor. Such a networkwould be defined by an unsymmetrical 1r circuit similar to that in FIG.3 wherein values of the admittances Y, and Y, would be unequal. Any ofthe networks in FIGS. 1, 4 and 5 may also have outer conductors withsquare or circular cross sections. The short circuit spaced I Z fromconnectors 7 and 8 may also be produced by omitting wall 16 andterminating conductors 4 and 5 in an open circuit spaced Z H4 from theconnectors. The scope and breadth of this invention is therefore to bedetermined from the following claims rather than the above detaileddescription.

What is claimed is:

1. Transmission line apparatus geometrically configured for supportingboth odd and even mode electromagnetic waves for matching a firstimpedance to a second impedance, comprising first and second parallelconductors;

a conductive ground plane enclosure supporting said parallel conductorstherein; said conductors being oriented in said enclosure with respectthereto for supporting odd and even modes therebetween, said parallelconductors having one ends thereof for connection to associatedimpedances to be matched;

means for connecting the first and second impedances between saidadjacent one ends of said first and second conductors, respectively, andsaid enclosure;

a movable wall of said enclosure electrically shortcircuiting saidparallel conductors together and to said enclosure for providing a firstshort circuit;

the lengths of parallel conductors between the one ends thereof and saidwall defining a length of transmission line of adjustable lengthprimarily supporting over its length only even modes;

a third conductor electrically movably contacting both of said parallelconductors at second adjacent points thereon between said one endsthereof and said wall for providing a second short circuit, the lengthof parallel conductors between the one ends thereof and said thirdconductor defining a length of transmission line of adjustable lengthsupporting both even and odd modes; and

a rod extending slidably through said wall and between said parallelconductors and being connected to said third conductor for moving theposition of the latter and the second short circuit provided therebyalong said parallel conductors.

2. Transmission line apparatus geometrically configured for supportingboth odd and even mode electromagnetic waves for matching a firstimpedance to a second impedance, comprising first and second parallelconductors;

a conductive ground plane enclosure supporting said parallel conductorstherein; said conductors being oriented in said enclosure with respectthereto for supporting odd and even modes therebetween, said parallelconductors having one ends thereof for connection to associatedimpedances to be matched;

means for connecting the first and second impedances between saidadjacent one ends of said first and second conductors, respectively, andsaid enclosure;

a movable wall of said enclosure electrically shortcircuiting saidparallel conductors together and to said enclosure for providing a firstshort circuit;

the lengths of parallel conductors between the one ends thereof and saidwall defining a length of transmission line of adjustable lengthprimarily supporting over its length only even modes;

a third conductor electrically movably contacting both of said parallelconductors at second adjacent points thereon between said one endsthereof and said wall for providing a second short circuit, the lengthof parallel conductors between the one ends thereof and said thirdconductor defining a length of transmission line of adjustable lengthsupporting both even and odd modes; and

a fourth conductor electrically connecting and shortcircuiting saidparallel conductors together and being located approximatelyintermediate said wall and said third conductor.

3. Transmission line apparatus geometrically configured for supportingboth odd and. even mode electromagnetic waves for matching a firstimpedance to a second impedance, comprising first and second parallelconductors that are rods having unequal diameters;

a conductive ground plane enclosure supporting said parallel conductorrods therein; said conductor rods being oriented with respect to saidground plane enclosure for supporting odd and even modes therebetween,said parallel conductor rods having first adjacent points thereon forconnection to the associated impedances to be matched;

first means electrically short-circuiting said parallel conductor rodstogether; and

second means electrically short-circuiting said parallel conductor rodstogether and to said ground plane;

the positions of said first and second short circuits provided by saidfirst and second short-circuiting means being independently movablealong said parallel conductor rods for tuning the apparatus.

4. An impedance matching network comprising a first transmission linesection supporting a combination of odd and even modes and comprisinglengths of a first ground plane and a pair of parallel conductors;

a second transmission line section;

first and second means producing short circuits on said first and secondtransmission line sections, respectively, for defining the electricallengths of the associated line sections; and

means for connecting impedances to be matched to each of said linesections at adjacent points that are spaced away from the ends ofassociated parallel conductors thereof.

5. An impedance matching network comprising a first transmission linesection supporting a combination of odd and even modes and comprisinglengths of a first ground plane and a pair of parallel conductors;

a second transmission line section comprising a second ground planeoriented with respect to said first ground plane for supportingelectromagnetic fields therebetween;

first and second means producing short circuits on said first and secondtransmission line sections, respectively, for defining the electricallength of the associated line sections; and

means for connecting impedances to be matched t each of said linesections.

6. An impedance matching network comprising a first transmission linesection supporting a combination of odd and even modes and comprisinglengths of a first ground plane enclosure and a pair of parallelconductors, said first ground plane being an enclosure supporting saidparallel conductors therein;

a second transmission line section comprising a second ground planeenclosure supporting said first enclosure therein and being orientedwith respect to the latter for supporting electromagnetic fieldstherebetween;

a first contact electrically connecting and shortcircuiting both of saidparallel conductors to said first ground plane enclosure, said firsttransmission line section comprising the short-circuited lengths of saidparallel conductors and said first ground plane enclosure;

means producing a short circuit on said second transmission line sectionfor defining the electrical length thereof; and

means for connecting impedances to be matched to each of said linesections.

7. An impedance matching network comprising a first transmission linesection supporting a combination of odd and even modes and comprisinglengths of a first ground plane enclosure and a pair of parallelconductors;

a second transmission line section comprising a second ground plane thatis oriented with respect to said first ground plane forsupportingelectromagnetic fields therebetween;

a first contact electrically connecting and shortcircuiting both of saidparallel conductors to said first ground plane for defining theelectrical length of said first line section, said first transmissionline section comprising the short-circuited lengths of said parallelconductors and said first ground plane;

a second contact electrically connecting said first and second groundplanes together for defining the electrical length of said second linesection, said second transmission line section comprising theshort-circuited lengths of said first and second ground planes; and

means for connecting impedances to be matched to each of said linesections;

said first ground plane being located between, spaced from, and parallelto said second ground plane and the plane defined-by said conductors.

8. Apparatus according to claim 2 wherein said fourth short circuitingconductor extends between said parallel conductors and connects thelatter together over the lengths thereof between said third conductorand said wall.

9. Apparatus according to claim 4 wherein said first ground plane is anenclosure supporting said parallel conductors therein and said firstshort circuiting means comprises a movable wall in said enclosure, saidwall being electrically connected to both of said conductors and to saidenclosure and positioned between the connection points and adjacent oneends of said parallel conductors, said first transmission line sectioncomprising the short circuited length of said parallel conductorsbetween said wall and said connection points.

10. Apparatus according to claim 9 wherein said second short circuitingmeans comprises an electrically conductive trombone sliding structureextending over and electrically connected to the other ends of saidparallel conductors, said second transmission line section comprisingthe short circuited length of said parallel conductors between saidtrombone structure and said connection points.

1 1. Apparatus according to claim 5 wherein said first short circuitingmeans comprises a first contact electrically connecting both of saidparallel conductors and said first ground plane together, said firsttransmission line section comprising the short circuited lengths of saidparallel conductors and said first ground plane.

12. Apparatus according to claim 11 wherein said second short circuitingmeans comprises a second contact electrically connecting said first andsecond ground planes together, said second transmission line sectioncomprising the short circuited lengths of said first and second groundplanes.

13. Apparatus according to claim 6 wherein said short circuiting meanscomprises a second contact electrically connecting said first and secondenclosures, said second line section comprising the short circuitedlengths of said first and second enclosures.

14. Apparatus according to claim 13 wherein said first and secondcontacts are movable in said enclosures for varying the electricallengths of the associated line sections and matching impedancesconnected thereto.

15. Apparatus according to claim 7 wherein a first impedance isconnected between one of said parallel conductors and said first groundplane and a second impedance to be matched to the first impedance isconnected between the other one of said parallel conductors and saidsecond ground plane.

16. Apparatus according to claim 15 wherein said line sections arestripline circuits, said first ground plane extending around saidconductors over the lengths thereof, said second ground plane alsoextending around said first ground plane over the length thereof.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,745,433 Dated July 10, 1973 Inventoflsy Robert G. Rogers It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 10, "Y should read Y column 2, line 18, "Y should read YColumn 5, equation (3) should read 1 1 11 1 J'[ 3( J' l j J/C j( 1 3LJJ] column 5, equation (4) should read I 2 2 B1 GiB GLB iG LcB BL) (GGL) 1/(GL G and column 5, equation (5 should read t 3 l i L [.(Bi 13 1GL)2]/(GL il-"- Column 8, line 35, the numeral "95" should read 93 .7

Signed and sealed this 20th day of August 197A.

(SEAL) Atte'st: r

McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-1OSO(10-69) USCQMM-DC 60376 9" u.l. covnnulur nnmue omclll" O'JN-IJI

1. Transmission line apparatus geometrically configured for supportingboth odd and even mode electromagnetic waves for matching a firstimpedance to a second impedance, comprising first and second parallelconductors; a conductive ground plane enclosure supporting said parallelconductors therein; said conductors being oriented in said enclosurewith respect thereto for supporting odd and even moDes therebetween,said parallel conductors having one ends thereof for connection toassociated impedances to be matched; means for connecting the first andsecond impedances between said adjacent one ends of said first andsecond conductors, respectively, and said enclosure; a movable wall ofsaid enclosure electrically short-circuiting said parallel conductorstogether and to said enclosure for providing a first short circuit; thelengths of parallel conductors between the one ends thereof and saidwall defining a length of transmission line of adjustable lengthprimarily supporting over its length only even modes; a third conductorelectrically movably contacting both of said parallel conductors atsecond adjacent points thereon between said one ends thereof and saidwall for providing a second short circuit, the length of parallelconductors between the one ends thereof and said third conductordefining a length of transmission line of adjustable length supportingboth even and odd modes; and a rod extending slidably through said walland between said parallel conductors and being connected to said thirdconductor for moving the position of the latter and the second shortcircuit provided thereby along said parallel conductors.
 2. Transmissionline apparatus geometrically configured for supporting both odd and evenmode electromagnetic waves for matching a first impedance to a secondimpedance, comprising first and second parallel conductors; a conductiveground plane enclosure supporting said parallel conductors therein; saidconductors being oriented in said enclosure with respect thereto forsupporting odd and even modes therebetween, said parallel conductorshaving one ends thereof for connection to associated impedances to bematched; means for connecting the first and second impedances betweensaid adjacent one ends of said first and second conductors,respectively, and said enclosure; a movable wall of said enclosureelectrically short-circuiting said parallel conductors together and tosaid enclosure for providing a first short circuit; the lengths ofparallel conductors between the one ends thereof and said wall defininga length of transmission line of adjustable length primarily supportingover its length only even modes; a third conductor electrically movablycontacting both of said parallel conductors at second adjacent pointsthereon between said one ends thereof and said wall for providing asecond short circuit, the length of parallel conductors between the oneends thereof and said third conductor defining a length of transmissionline of adjustable length supporting both even and odd modes; and afourth conductor electrically connecting and short-circuiting saidparallel conductors together and being located approximatelyintermediate said wall and said third conductor.
 3. Transmission lineapparatus geometrically configured for supporting both odd and even modeelectromagnetic waves for matching a first impedance to a secondimpedance, comprising first and second parallel conductors that are rodshaving unequal diameters; a conductive ground plane enclosure supportingsaid parallel conductor rods therein; said conductor rods being orientedwith respect to said ground plane enclosure for supporting odd and evenmodes therebetween, said parallel conductor rods having first adjacentpoints thereon for connection to the associated impedances to bematched; first means electrically short-circuiting said parallelconductor rods together; and second means electrically short-circuitingsaid parallel conductor rods together and to said ground plane; thepositions of said first and second short circuits provided by said firstand second short-circuiting means being independently movable along saidparallel conductor rods for tuning the apparatus.
 4. An impedancematching network comprising a first transmission line section supportinga combination of odd and even mOdes and comprising lengths of a firstground plane and a pair of parallel conductors; a second transmissionline section; first and second means producing short circuits on saidfirst and second transmission line sections, respectively, for definingthe electrical lengths of the associated line sections; and means forconnecting impedances to be matched to each of said line sections atadjacent points that are spaced away from the ends of associatedparallel conductors thereof.
 5. An impedance matching network comprisinga first transmission line section supporting a combination of odd andeven modes and comprising lengths of a first ground plane and a pair ofparallel conductors; a second transmission line section comprising asecond ground plane oriented with respect to said first ground plane forsupporting electromagnetic fields therebetween; first and second meansproducing short circuits on said first and second transmission linesections, respectively, for defining the electrical length of theassociated line sections; and means for connecting impedances to bematched to each of said line sections.
 6. An impedance matching networkcomprising a first transmission line section supporting a combination ofodd and even modes and comprising lengths of a first ground planeenclosure and a pair of parallel conductors, said first ground planebeing an enclosure supporting said parallel conductors therein; a secondtransmission line section comprising a second ground plane enclosuresupporting said first enclosure therein and being oriented with respectto the latter for supporting electromagnetic fields therebetween; afirst contact electrically connecting and short-circuiting both of saidparallel conductors to said first ground plane enclosure, said firsttransmission line section comprising the short-circuited lengths of saidparallel conductors and said first ground plane enclosure; meansproducing a short circuit on said second transmission line section fordefining the electrical length thereof; and means for connectingimpedances to be matched to each of said line sections.
 7. An impedancematching network comprising a first transmission line section supportinga combination of odd and even modes and comprising lengths of a firstground plane enclosure and a pair of parallel conductors; a secondtransmission line section comprising a second ground plane that isoriented with respect to said first ground plane for supportingelectromagnetic fields therebetween; a first contact electricallyconnecting and short-circuiting both of said parallel conductors to saidfirst ground plane for defining the electrical length of said first linesection, said first transmission line section comprising theshort-circuited lengths of said parallel conductors and said firstground plane; a second contact electrically connecting said first andsecond ground planes together for defining the electrical length of saidsecond line section, said second transmission line section comprisingthe short-circuited lengths of said first and second ground planes; andmeans for connecting impedances to be matched to each of said linesections; said first ground plane being located between, spaced from,and parallel to said second ground plane and the plane defined by saidconductors.
 8. Apparatus according to claim 2 wherein said fourth shortcircuiting conductor extends between said parallel conductors andconnects the latter together over the lengths thereof between said thirdconductor and said wall.
 9. Apparatus according to claim 4 wherein saidfirst ground plane is an enclosure supporting said parallel conductorstherein and said first short circuiting means comprises a movable wallin said enclosure, said wall being electrically connected to both ofsaid conductors and to said enclosure and positioned between theconnection points and adjacent one ends of said parallel conductors,said firSt transmission line section comprising the short circuitedlength of said parallel conductors between said wall and said connectionpoints.
 10. Apparatus according to claim 9 wherein said second shortcircuiting means comprises an electrically conductive trombone slidingstructure extending over and electrically connected to the other ends ofsaid parallel conductors, said second transmission line sectioncomprising the short circuited length of said parallel conductorsbetween said trombone structure and said connection points. 11.Apparatus according to claim 5 wherein said first short circuiting meanscomprises a first contact electrically connecting both of said parallelconductors and said first ground plane together, said first transmissionline section comprising the short circuited lengths of said parallelconductors and said first ground plane.
 12. Apparatus according to claim11 wherein said second short circuiting means comprises a second contactelectrically connecting said first and second ground planes together,said second transmission line section comprising the short circuitedlengths of said first and second ground planes.
 13. Apparatus accordingto claim 6 wherein said short circuiting means comprises a secondcontact electrically connecting said first and second enclosures, saidsecond line section comprising the short circuited lengths of said firstand second enclosures.
 14. Apparatus according to claim 13 wherein saidfirst and second contacts are movable in said enclosures for varying theelectrical lengths of the associated line sections and matchingimpedances connected thereto.
 15. Apparatus according to claim 7 whereina first impedance is connected between one of said parallel conductorsand said first ground plane and a second impedance to be matched to thefirst impedance is connected between the other one of said parallelconductors and said second ground plane.
 16. Apparatus according toclaim 15 wherein said line sections are stripline circuits, said firstground plane extending around said conductors over the lengths thereof,said second ground plane also extending around said first ground planeover the length thereof.